In a numerically controlled machine tool such as a numerically controlled automatic lathe, a long bar material may be used as a material when a relatively small product is machined. As a machining method of this type based on the numerically controlled automatic lathe, there has conventionally been known an art of feeding a bar material to a portion to be machined from a rear side of the numerically controlled automatic lathe by a bar material supply device, and rotating the bar material together with a spindle to cut and machine a front end of the bar material into a predetermined shape (e.g., see Patent Reference 1).    Patent Reference 1: JP A 2001-246502 (refer to FIG. 1 of the drawings, and a paragraph [0008] of the description).
FIG. 14 is an explanatory plan view of an entire configuration of the bar supply device according to the conventional example.
The numerically controlled automatic lathe equipped with the bar material supply device shown in FIG. 14 includes a spindle 230 which is freely back and forth movable in the same direction as that of an axis C of the spindle and a guide bush 232 arranged before the spindle 230, and machines a bar material W by a working tool in a supported state of a front end of the bar material projected from the spindle 230 on the guide bush 232.
As shown in FIG. 14, the bar material supply device 33 includes a push rod 350 constituted separately of the numerically controlled automatic lathe and arranged after (left of a paper surface of FIG. 14) the same to push the long bar material W, and driving means 360 for moving this push rod 350 back and forth. The driving means 360 includes a drive body 361 such as a stepping motor or a servo motor capable of precisely. adjusting a rotational angle position, a driving pulley 362 which is rotated by the drive body 361, a driven pulley 363 arranged in a position opposed to the driving pulley 362, and an endless cableway 364 such as a belt or a change wound between the driving pulley 362 and the driven pulley 363, and the push rod 350 is connected to the endless cableway 364. In a state where a rear end of the bar material W is gripped to rotate by a finger chuck 351 of a front end (right end of the paper surface of FIG. 14), the drive body 361 is driven to move the push rod 350 back and froth on the spindle axis while the endless cableway 364 travels, thereby feeding the bar material W to the spindle 230.
However, the aforementioned bar material supply device has a problem that a mechanism of moving the bar material back and forth is complex, large, and high in cost.
In the aforementioned numerically controlled automatic lathe equipped with the guide bush 232, a short material that cannot be machined any more and must accordingly be discarded as an end material because of a positional relation between the guide bush 232 and a chuck 231 of the spindle 230, a length or a cut-off width of a component to be machined, or the like is left.
FIG. 15 shows a state of the bar material W at-an end of machining when the bar material is machined by the numerically controlled automatic lathe equipped with the guide bush. A short material (hereinafter, such short bar material will be referred as “bar material w” to be differentiated from long “bar material W”) that has become an end material is left between the guide bush 232 and the chuck 231 of the spindle 230.
A length of the bar material w is a sum of a distance from a front end of the bar material w in which a product P has been cut off by a cutting-off tool T3 to the chuck 231, a gripping length of the bar material w by the chuck 231, a distance from the chuck 231 to the front end of the push rod 350, and a gripping length of the push rod 350 by the finger chuck 351.
Thus, in the numerically controlled automatic lathe equipped with the guide bush 232, the bar material w of a length 1 impossible to be machined is left even while the product P can be produced more, creating a problem of a reduction in material yield.
Additionally, machining of such a bar material w can be carried out by another numerically controlled automatic lathe having no guide bush. However, when the aforementioned conventional bar material supply device complex in configuration is used, a new problem of a n increase in machining cost of the bar material w is created.
Accordingly, to simplify and miniaturize the aforementioned bar material supply device, there has been proposed a n art of eliminating the endless cableway such as the chain or the belt from the bar material supply device, holding the bar material between two rollers arranged to face each other, and moving the bar material back and forth by rotating the rollers (e.g., see Patent References 2, 3).    Patent Reference 2: JP A 7-60503 (refer to FIG. 2 of the drawings and a paragraph [0010] of the description).    Patent Reference 3: JP A 2002-187001 (refer to FIG. 2 of the drawings and a paragraph [0015] of the description).
According to the art of the Patent Reference 2, as can be understood from FIG. 2, the bar material is held between two carrier rollers 4, 4 arranged to face each other, and the bar material to be machined is fed by rotating the carrier rollers 4, 4.
According to the art of the Patent Reference 3, as can be understood from FIG. 3, the bar material is fed by two carrier rollers 8a, 8b for holding the same therebetween. According to the art described in the Patent Reference 3, the carrier rollers 8a, 8b are both connected to a driving motor 43, and driving force is transmitted from the driving motor 43 to the carrier rollers 8a, 8b. When the bar material is machined, as shown in FIG. 6, the carrier rollers 8a, 8b are retreated to positions for not interfering with the bar material.